What is flux in jewellery making?
By Jared James · Last updated 21 May 2026
Definition
Flux is a material, usually a liquid, paste or powder, applied to metal before soldering to prevent oxidation and help solder flow cleanly into the joint. When metal is heated it oxidises quickly, and that oxide layer stops solder bonding properly. Flux creates a chemical barrier that slows oxidation at the join and lowers the surface tension of molten solder so it runs freely along the seam. Borax dissolved in water is the classic choice for silver and gold work, though commercial paste fluxes are also widely used.
Frequently asked questions
- Why do jewellers use flux when soldering?
- Heating metal causes oxidation, and oxidised surfaces repel solder. Flux keeps the join area clean long enough for the solder to flow, bond and cool properly. Without it, solder beads up or refuses to stick, and the join is unreliable.
- What is the most common flux for silver and gold?
- Borax mixed with water into a paste or liquid is the traditional choice and still widely used. Commercial flux pastes designed specifically for precious metal work are also popular because they are easier to apply precisely and have consistent flow temperatures.
- Is flux toxic?
- Most jewellery fluxes are mildly corrosive and should not be ingested, and the fumes produced when flux burns off during soldering should not be inhaled. Working with good ventilation is straightforward and necessary for any soldering work, flux or not.
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